Since the December “underwear bomb” plot, U.S. airports have rolled out a fleet of advanced imaging devices, including backscatter X-ray screeners and millimeter-wave body scanners. The gaze of all-seeing eyes could soon become even more penetrating, as physicists and engineers exploit new kinds of light that can see through barriers and clothing.
At the airport, the next generation of body scanners may rely on terahertz radiation, or T-rays. Unlike X-rays, T-rays are not energetic enough to strip electrons from atoms, making them safer for humans. They are also exceptionally sensitive to chemical structure, easily able to distinguish over-the-counter drugs from illegal substances. Before T-ray cameras and scanners can become a reality, however, researchers need to learn to control the radiation more precisely. Electrical engineer Qing Hu at MIT demonstrated a method to tune a terahertz laser by changing the diameter of the cavity emitting the rays, allowing him to finesse the beam to specific frequencies. And researchers at Texas A&M and Rice University are learning to control the rays by adjusting the temperature of a semiconductor film they pass through.
Other scanners may find better use in the field. At the University of Utah, engineer Neal Patwari and doctoral candidate Joey Wilson are using radio waves to see through obstacles. Their network of radio transceivers measures the signal strength to reveal the locations of people or objects in the area. The system can find targets in the dark and through walls, smoke, or trees. Patwari and Wilson are currently working to expand the transceivers’ range, currently 50 feet. For now the detector can follow only a single individual, Patwari says, “but we will soon be able to track multiple people or objects and tell the difference between them.” The technology could find applications in fire rescues, hostage situations, and border security.
